musical_beat_detector.h

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#pragma once
 
#include "fl/stl/int.h"
#include "fl/stl/vector.h"
#include "fl/stl/deque.h"
#include "fl/stl/noexcept.h"
 
namespace fl {
namespace audio {
namespace detector {

struct MusicalBeatDetectorConfig {
    float minBPM = 50.0f;

    float maxBPM = 250.0f;

    float minBeatConfidence = 0.5f;

    float bpmSmoothingAlpha = 0.9f;

    u32 sampleRate = 22050;

    u32 samplesPerFrame = 512;

    u32 maxIBIHistory = 8;
};

class MusicalBeat {
public:
    MusicalBeat() FL_NOEXCEPT;
    explicit MusicalBeat(const MusicalBeatDetectorConfig& config);
    ~MusicalBeat() FL_NOEXCEPT;

    void configure(const MusicalBeatDetectorConfig& config);

    void processSample(bool onsetDetected, float onsetStrength);

    bool isBeat() const;

    float getBPM() const;

    float getBeatConfidence() const;

    float getAverageIBI() const;

    void reset();

    struct Stats {
        u32 totalOnsets = 0;        // Total onsets detected (lifetime)
        u32 validatedBeats = 0;     // Onsets validated as beats (lifetime)
        u32 rejectedOnsets = 0;     // Onsets rejected (not rhythmic)
        float currentBPM = 0.0f;    // Current BPM estimate
        float averageIBI = 0.0f;    // Average inter-beat interval (seconds)
        u32 ibiCount = 0;           // Number of IBIs in history
    };
 
    const Stats& getStats() const { return mStats; }
 
private:
    bool validateBeat(float onsetStrength);

    float calculateBeatConfidence(float currentIBI);

    void updateBPMEstimate();

    bool isValidIBI(float ibi) const;

    float calculateIBIStdDev() const;
 
    MusicalBeatDetectorConfig mConfig;
    Stats mStats;

    bool mBeatDetected = false;

    float mLastBeatConfidence = 0.0f;

    float mCurrentBPM = 120.0f;

    u32 mLastBeatFrame = 0;

    u32 mCurrentFrame = 0;

    deque<u32> mIBIHistory;

    float mAverageIBI = 0.0f;
};
 
} // namespace detector
} // namespace audio
} // namespace fl